/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.handler.traffic;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPromise;

import java.util.ArrayDeque;
import java.util.concurrent.TimeUnit;

/**
 * <p>
 * This implementation of the {@link AbstractTrafficShapingHandler} is for
 * channel traffic shaping, that is to say a per channel limitation of the
 * bandwidth.
 * </p>
 * <p>
 * Note the index used in
 * {@code OutboundBuffer.setUserDefinedWritability(index, boolean)} is <b>1</b>.
 * </p>
 *
 * <p>
 * The general use should be as follow:
 * </p>
 * <ul>
 * <li>
 * <p>
 * Add in your pipeline a new ChannelTrafficShapingHandler.
 * </p>
 * <p>
 * <tt>ChannelTrafficShapingHandler myHandler = new ChannelTrafficShapingHandler();</tt>
 * </p>
 * <p>
 * <tt>pipeline.addLast(myHandler);</tt>
 * </p>
 *
 * <p>
 * <b>Note that this handler has a Pipeline Coverage of "one" which means a new
 * handler must be created for each new channel as the counter cannot be shared
 * among all channels.</b>.
 * </p>
 *
 * <p>
 * Other arguments can be passed like write or read limitation (in bytes/s where
 * 0 means no limitation) or the check interval (in millisecond) that represents
 * the delay between two computations of the bandwidth and so the call back of
 * the doAccounting method (0 means no accounting at all).
 * </p>
 *
 * <p>
 * A value of 0 means no accounting for checkInterval. If you need traffic
 * shaping but no such accounting, it is recommended to set a positive value,
 * even if it is high since the precision of the Traffic Shaping depends on the
 * period where the traffic is computed. The highest the interval, the less
 * precise the traffic shaping will be. It is suggested as higher value
 * something close to 5 or 10 minutes.
 * </p>
 *
 * <p>
 * maxTimeToWait, by default set to 15s, allows to specify an upper bound of
 * time shaping.
 * </p>
 * </li>
 * <li>In your handler, you should consider to use the
 * {@code channel.isWritable()} and {@code channelWritabilityChanged(ctx)} to
 * handle writability, or through
 * {@code future.addListener(new GenericFutureListener())} on the future
 * returned by {@code ctx.write()}.</li>
 * <li>
 * <p>
 * You shall also consider to have object size in read or write operations
 * relatively adapted to the bandwidth you required: for instance having 10 MB
 * objects for 10KB/s will lead to burst effect, while having 100 KB objects for
 * 1 MB/s should be smoothly handle by this TrafficShaping handler.
 * </p>
 * </li>
 * <li>
 * <p>
 * Some configuration methods will be taken as best effort, meaning that all
 * already scheduled traffics will not be changed, but only applied to new
 * traffics.
 * </p>
 * <p>
 * So the expected usage of those methods are to be used not too often,
 * accordingly to the traffic shaping configuration.
 * </p>
 * </li>
 * </ul>
 */
public class ChannelTrafficShapingHandler extends AbstractTrafficShapingHandler
{
    private final ArrayDeque<ToSend> messagesQueue = new ArrayDeque<ToSend>();

    private long queueSize;

    /**
     * Create a new instance.
     *
     * @param writeLimit 0 or a limit in bytes/s
     * @param readLimit 0 or a limit in bytes/s
     * @param checkInterval The delay between two computations of performances
     *        for channels or 0 if no stats are to be computed.
     * @param maxTime The maximum delay to wait in case of traffic excess.
     */
    public ChannelTrafficShapingHandler(long writeLimit, long readLimit,
            long checkInterval, long maxTime)
    {
        super(writeLimit, readLimit, checkInterval, maxTime);
    }

    /**
     * Create a new instance using default max time as delay allowed value of
     * 15000 ms.
     *
     * @param writeLimit 0 or a limit in bytes/s
     * @param readLimit 0 or a limit in bytes/s
     * @param checkInterval The delay between two computations of performances
     *        for channels or 0 if no stats are to be computed.
     */
    public ChannelTrafficShapingHandler(long writeLimit, long readLimit,
            long checkInterval)
    {
        super(writeLimit, readLimit, checkInterval);
    }

    /**
     * Create a new instance using default Check Interval value of 1000 ms and
     * max time as delay allowed value of 15000 ms.
     *
     * @param writeLimit 0 or a limit in bytes/s
     * @param readLimit 0 or a limit in bytes/s
     */
    public ChannelTrafficShapingHandler(long writeLimit, long readLimit)
    {
        super(writeLimit, readLimit);
    }

    /**
     * Create a new instance using default max time as delay allowed value of
     * 15000 ms and no limit.
     *
     * @param checkInterval The delay between two computations of performances
     *        for channels or 0 if no stats are to be computed.
     */
    public ChannelTrafficShapingHandler(long checkInterval)
    {
        super(checkInterval);
    }

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception
    {
        TrafficCounter trafficCounter = new TrafficCounter(this, ctx.executor(),
                "ChannelTC" + ctx.channel().hashCode(), checkInterval);
        setTrafficCounter(trafficCounter);
        trafficCounter.start();
        super.handlerAdded(ctx);
    }

    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception
    {
        trafficCounter.stop();
        // write order control
        synchronized (this)
        {
            if (ctx.channel().isActive())
            {
                for (ToSend toSend : messagesQueue)
                {
                    long size = calculateSize(toSend.toSend);
                    trafficCounter.bytesRealWriteFlowControl(size);
                    queueSize -= size;
                    ctx.write(toSend.toSend, toSend.promise);
                }
            }
            else
            {
                for (ToSend toSend : messagesQueue)
                {
                    if (toSend.toSend instanceof ByteBuf)
                    {
                        ((ByteBuf) toSend.toSend).release();
                    }
                }
            }
            messagesQueue.clear();
        }
        releaseWriteSuspended(ctx);
        releaseReadSuspended(ctx);
        super.handlerRemoved(ctx);
    }

    private static final class ToSend
    {
        final long relativeTimeAction;

        final Object toSend;

        final ChannelPromise promise;

        private ToSend(final long delay, final Object toSend,
                final ChannelPromise promise)
        {
            relativeTimeAction = delay;
            this.toSend = toSend;
            this.promise = promise;
        }
    }

    @Override
    void submitWrite(final ChannelHandlerContext ctx, final Object msg,
            final long size, final long delay, final long now,
            final ChannelPromise promise)
    {
        final ToSend newToSend;
        // write order control
        synchronized (this)
        {
            if (delay == 0 && messagesQueue.isEmpty())
            {
                trafficCounter.bytesRealWriteFlowControl(size);
                ctx.write(msg, promise);
                return;
            }
            newToSend = new ToSend(delay + now, msg, promise);
            messagesQueue.addLast(newToSend);
            queueSize += size;
            checkWriteSuspend(ctx, delay, queueSize);
        }
        final long futureNow = newToSend.relativeTimeAction;
        ctx.executor().schedule(new Runnable()
        {
            @Override
            public void run()
            {
                sendAllValid(ctx, futureNow);
            }
        }, delay, TimeUnit.MILLISECONDS);
    }

    private void sendAllValid(final ChannelHandlerContext ctx, final long now)
    {
        // write order control
        synchronized (this)
        {
            ToSend newToSend = messagesQueue.pollFirst();
            for (; newToSend != null; newToSend = messagesQueue.pollFirst())
            {
                if (newToSend.relativeTimeAction <= now)
                {
                    long size = calculateSize(newToSend.toSend);
                    trafficCounter.bytesRealWriteFlowControl(size);
                    queueSize -= size;
                    ctx.write(newToSend.toSend, newToSend.promise);
                }
                else
                {
                    messagesQueue.addFirst(newToSend);
                    break;
                }
            }
            if (messagesQueue.isEmpty())
            {
                releaseWriteSuspended(ctx);
            }
        }
        ctx.flush();
    }

    /**
     * @return current size in bytes of the write buffer.
     */
    public long queueSize()
    {
        return queueSize;
    }
}
